During the night of 26-27 October 2012, the TAROT telescope observed the galaxy NGC 1365. Inspection of the images by Alain Klotz, astrophysicist at the Institute for Research in Astrophysics and Planetology (IRAP) and professor at the University of Toulouse, revealed the presence of a new star near the center of the galaxy. The presence of the new star was quickly confirmed by an image taken by the French amateur astronomer Emmanuel Conseil using the SLOOH telescope. Mickael Childress, astronomer at the National University of Australia, characterized the nature of the star as a type Ia supernova and the International Astronomical Union then officially registered it 2012fr.
The theory that explains the type Ia supernova phenomenon involves a pair of stars, one of which sucks up the gas from the other. When the star that sucks in the gas exceeds a critical mass, it explodes violently, ejecting its gas at speeds of about 10,000 kilometres per second. As the gas expands, the supernova becomes brighter and brighter. A fortnight after the explosion, the optical brightness of the supernova generally reaches the brightness of the entire galaxy, that is to say the equivalent of about 10 billion times the brightness of the Sun. The interesting feature of type Ia supernovae is that their maximum brightness allows us to estimate the distances of distant galaxies in our Universe.
The galaxy NGC 1365, in which supernova 2012fr exploded, shows a characteristic spiral shape that is highly aesthetic and appreciated by lovers of spectacular images of the cosmos. This galaxy was also studied in detail with the Hubble Space Telescope during the 1990s, which made it possible to establish its distance very precisely thanks to the observation of about forty Cepheid-type stars. Located 61 million light years away from us, the Cepheids of NGC 1365 are at the limit of the space telescope’s capabilities, which is the upper limit of distance estimation by the Cepheid method.
The presence of supernova 2012fr in one of the most distant galaxies whose distance has been precisely measured with the Cepheids will allow to refine the calibration of the distance scale for the supernovae maximum brightness method. This calibration is important for cosmological studies because supernovae allow distances to be estimated up to several billion light years and have been used in particular to measure the acceleration of the expansion of the Universe which led to the Nobel Prize in Physics in 2011.
The TAROT telescope, which enabled the discovery of the 2012fr supernova, is located in the European Southern Observatory (ESO) at the Silla site in Chile. A twin TAROT telescope is located in France on the Calern plateau north of Nice. The TAROT telescopes are robotic and operate autonomously without human presence during the night. They have exceptional scientific performance compared to their relatively small diameter of 25 centimetres.
The French team of astronomers who discovered supernova 2012fr usually use the TAROT telescopes to study other cosmic explosions, gamma-ray bursts, which are even more violent than supernovae. When there are no gamma-ray bursts to observe, routine observations allow the precise study of specific astronomical phenomena over several years or allow the discovery of supernovae as was the case for 2012fr.
- Alain Klotz, E-mail: email@example.com